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  #1  
Old 05-22-2010, 05:11 PM
guru200773 guru200773 is offline
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Default QUIESCENT in transistor

Can any one explain quiescent in transistor..? pls thank u
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  #2  
Old 05-23-2010, 01:08 AM
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Ron H Ron H is offline
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Quiescent means "at rest". In a transistor circuit, the quiescent state is defined by the voltages and currents present in the circuit when the power supply is on and stable, and no signal is applied.
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Old 05-23-2010, 06:47 AM
guru200773 guru200773 is offline
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oh ok ok friend but how it related in Classes of amplifiers? Is there any relation between this quiescent state and load line?
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Old 05-23-2010, 05:09 PM
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A class-A single transistor conducts a high current all the time. The current is modulated with the signal.
A class-B cxircuit has two usually complementary transistors (one is NPN and the other is PNP). They do not have an input bias voltage so they are completely cutoff at rest. They have crossover distortion.
A class-AB circuit usually has a complementary pair of transistors that are biased with a low quiescent currenty so they are always turned on a little with very low crossover distortion.

You can look in a text book or in Google to see a class-C and a class-D amplifier description.
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Old 05-23-2010, 05:12 PM
guru200773 guru200773 is offline
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ya i know this friend... but what is load line?
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Old 05-23-2010, 05:32 PM
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You need to study the basics of electronics to know what is a load line.
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Old 05-24-2010, 03:29 AM
logicman112 logicman112 is offline
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Load line is the relationship of output voltage and current. If you consider a transistor as a two-ports network, it has input and output ports. Sometimes the relationship of output votage, means, vCE and output current means, ic, is like a line and it happens when transistor is used with resistive components not components with reactance like capacitors or inductors(Sometime those exist but they behave like short/open circuits and it is OK then).

Load line has DC and AC mathematical components and it is drawn with characteristic output diagram of transistor and true voltage and current of the transistor is on the characteristic curve and load line at the same time.
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  #8  
Old 05-24-2010, 12:16 PM
guru200773 guru200773 is offline
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thank u logic man
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Old 05-25-2010, 10:27 AM
logicman112 logicman112 is offline
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you are welcome. I will try to clarify the subject more, please ask more questions and I will try to answer. I lack time unfortunately but I wish i could review the questions. The worse is that this site does not let you review your previous posts, makes it very difficult to follow up our previous notes....

quiescent means static values. Transistor is drived by some DC voltage or current sources and some resistors. It makes you have some fixed DC voltages-currents for transistor and makes the transistor work in a specific region. Transistor has 3 basic regions to choose to work.

For small signal amplifying applications we drive it to Forward-Active-Region normally. In this region the signal AC voltage/current relations in Kierkoff's equations are linear which will lead to linear amplification.
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Old 05-25-2010, 04:36 PM
guru200773 guru200773 is offline
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sure dude i am a newbie so i will ask many silly question tooo
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